The invention relates non-destructive characterization of GaAs wafers and more specifically to a system for measuring carrier mobility and carrier concentration from on-wafer Hall-effect measurements of a patterned GaAs wafer during the fabrication sequence.
Resistivity (.rho.) mobility (.mu.), and carrier concentration (n) are acknowledged figures of merit for semiconductor materials. On a large wafer (e.g., 2 or 3 inches round, GaAs wafers), .rho., .mu. and n can vary as a function of position, and it is important to ascertain these variations before committing the wafer to full device fabrication. A relatively common modern procedure is to carry out automated resistivity mapping after ohmic contacts have been formed on the wafer, but before the rest of the processing has been completed. The resistivity mapping normally makes use of a dense set of van der Pauw patterns, which require only ohmic contacts. It is generally acknowledged that the parameters .mu. and n would be much more useful, but up to now their attainment using current test equipment has required cutting up the wafer in order to get enough pieces to fit between the pole pieces of a magnet. The present invention makes it possible to get such measurements without cutting up the wafer.
Measurements of conducting layer mobility and carrier concentration are important and useful parameters in the design and modeling of field effect devices. Designers are able to use this information to more effectively model device designs for improved performance and the information can provide a guide to process engineers for modification aimed at improved process uniformity. Methods which rely on C-V and I-V measurements of test structures have been developed to obtain carrier mobility and concentration. These methods require careful attention to measurement technique and are difficult to accurately implement.